The invention relates to a blade system for a scraped surface heat exchanger.
Scraped surface heat exchangers are particularly suitable for use in the foodstuff industry where they are used for refrigerating or heating fatty products, bakery products and dairy products, such as margarine emulsion and ice cream. A heat exchanger of this type includes a cylindrical treatment chamber, a rotor arranged in the chamber and a number of blade rows including a number of successively arranged blade scrapers mounted on the rotor so as to make the blades scrape the inner surface of the chamber during operation. A refrigerant or a heating medium, e.g. ammonia, freon, glycol, hot water or steam, is circulated on the outside of the treatment chamber and provides heat exchange by a conventional heat exchange process. The treated product is introduced under pressure at the one end of the heat exchanger and leaves the heat exchanger at its opposite end. The scraping of the product off the inner surface of the chamber during its passage through the heat exchanger thereby provides a considerably improved heat transmission.
In known apparatuses the blade scrapers are designed with apertures and/or slits and are secured to the rotor by use of pins or screws or combinations thereof. The use of this securing method makes it necessary to remove the rotor from the treatment chamber during control or replacement of the blades. This is a time consuming operation, and in view of the fact that the manufacturing process must be discontinued in the production line where the heat exchanger is arranged, the control and replacement of the blades are also associated with a considerable financial loss. Furthermore, such screws or pins with corresponding apertures or slits in the blades create dead spots wherein minor amounts of treated product and dirt may accumulate with an ensuing risk of bacteria growth.
GB published patent application No. 2,232,469 discloses such scraped surface heat exchanger wherein the blades are mounted on the rotor by use of hinge means. A similar heat exchanger is known from EP publication No. 400 700. In both cases it is necessary to remove the rotor from the treatment chamber to check or replace the scraper blades.
U.S. Pat. No. 3,385,354 describes, e.g. in FIG. 4, a scraped surface heat exchanger wherein the scraper blades are arranged in a V-shaped cut-out and wherein pins arranged on the rotor pass through apertures or recesses in the blades. Thus, in case of this known heat exchanger, it is also impossible to replace or check the blades without initially removing the rotor from the treatment chamber.